Fully closed headphones (circum-aural or supra-aural) are generally not seen in the current market. By fully closed it is meant that there are no venting or controlled acoustic leakages from the front volume to the outside, from the back volume to the outside or connecting the front and back volumes.
There are various reasons why a fully closed headphone acoustical architecture may not be the preferred acoustical system.                (1) The fully closed front volume will cause a DC pressure on the headphone driver, potentially causing permanent deformation of the diaphragm        (2) The fully closed acoustical system will be very susceptible to uncontrollable leakages occurring when the headphones are in use. A leakage may be introduced between the ear pad and the wearer's head and/or ear due to hair or glasses.        